1. Field of the Invention
The present invention relates to a mold mounting platen for use in an injection molding machine.
2. Description of the Related Art
An injection molding machine includes a movable platen which moves along several tie rods disposed perpendicularly to a stationary platen fixed to a base frame. Moreover, in a clamping mechanism of the injection molding machine, the movable platen and a rear platen are connected by a toggle mechanism. The extension of links of the toggle mechanism causes the tie rods to extend and generates clamping force.
FIG. 10 is a view showing a toggle clamping mechanism of a general prior art injection molding machine. Reference numeral 1 denotes a movable platen, and reference numeral 2 denotes a stationary platen. Moreover, reference numerals 3 denote tie rods. The movable platen 1 is configured to move along the tie rods 3 in the lateral direction in FIG. 10. The tie rods 3 are fixed to tie rod fixing portions 6 on a surface of the stationary platen 2 which is opposite from the movable platen 1 side.
A movable-side mold half 5 and a stationary-side mold half 4 are respectively provided on the movable platen 1 and the stationary platen 2 to face each other. Moreover, a toggle link mechanism 71 is provided on a side of the movable platen 1 which is opposite from the stationary platen 2. The toggle link mechanism 71 transmits the clamping force of the movable platen 1 side to the movable-side mold half 5.
As shown in FIG. 10, in the prior art injection molding machine, the tie rod fixing portions 6 to which the tie rods 3 are fixed are provided in four corner portions of the stationary platen 2, and toggle link supporting points 7 of the toggle link mechanism 71 are provided at two upper and lower outer positions on the movable platen 1. In the case where such a configuration is employed, the following problem may occur: the contact pressure at a junction surface 14 between the stationary-side mold half 4 and the movable-side mold half 5 increases with increasing distance from the center, and becomes low in a central region.
A number of techniques which have been developed to solve the above-described problem are disclosed in the patent documents below.
In a clamping mechanism for an injection molding machine disclosed in Japanese Patent Application Laid-Open No. H8-258103, square pyramid-shaped support mechanisms are used to support a stationary platen and a movable platen. Apex portions of the support mechanisms support the stationary platen and the movable platen so that clamping force may be generated in the central region.
In a mold clamping apparatus disclosed in Japanese Patent Application Laid-Open No. H11-170322, a groove for the prevention of distortion is provided between toggle link supporting points and a mold mounting surface to which a movable-side mold half is attached, so as to prevent distortion from occurring in the mold mounting surface.
Moreover, in a mold clamping apparatus for an injection molding machine disclosed in Japanese Patent Application Laid-Open No. 2007-253458, a detachable contact member is provided between each of a stationary platen, a movable platen and a peripheral portion of a corresponding clamping force transmission member. The contact member is attached or detached in accordance with the size of a mold to control the transmission of clamping force from the clamping force transmission members.
Further, in a mold clamping apparatus disclosed in Japanese Patent Application Laid-Open No. 2010-111018, extended portions are provided on the periphery of a mold mounting surface as contact pressure adjusting portions for reducing pressure differences occurring across a junction surface between a stationary-side mold half and a movable-side mold half.
In the clamping mechanism of the injection molding machine disclosed in Japanese Patent Application Laid-Open No. H8-258103 and the mold clamping apparatus disclosed in Japanese Patent Application Laid-Open No. H11-170322, a decrease in contact pressure in the central region can be reduced by pressing only in the central region or by providing a groove to inhibit the transmission of the clamping force in a peripheral region. Such configurations are suitable for cases where a mold is located only in the central region. However, in the case where a mold is vertically or horizontally long and reaches the outside of connecting portions of divided platens in Japanese Patent Application Laid-Open No. H8-258103 or a portion corresponding to the groove in Japanese Patent Application Laid-Open No. H11-170322, the transmission of the clamping force is weak in the peripheral region. Accordingly, dimensional errors or burrs may occur in molded parts (see FIG. 11).
In the mold clamping apparatus of the injection molding machine disclosed in Japanese Patent Application Laid-Open No. 2007-253458, the transmission of the clamping force to the peripheral region is controlled by attaching or detaching the contact members as clamping force transmission members. However, the contact members need to be provided as additional components. Accordingly, the complexity of the mechanism and the operation may increase as follows: mechanisms for attaching and detaching the contact members in accordance with mold size and the like need to be added; the contact members need to be attached or detached by hand operation; and the like.
In the mold clamping apparatus disclosed in Japanese Patent Application Laid-Open No. 2010-111018, bearing surfaces for connection are provided on the periphery. Thus, the mold clamping apparatus is suitable for vertically or horizontally long molds. However, the effect of concentrating the clamping force at the center is small. Accordingly, in the case where a mold is located only in a central portion, problems such as a decrease in the clamping force may occur.